1. Technical Field
The present invention relates to a projection type display device including lamp dimming and mechanical dimming, and a control method thereof
2. Related Art
In recent years, a projectors, which are a type of projection type display device which displays a display onto a large screen are widely used. The projectors are advantageous when a large screen is desired, however, there has been a problem in that it is difficult to obtain a sufficient contrast since a display contrast of the projector depends on a contrast in a liquid crystal light valve. Therefore, a technology has been known in which luminance of a light source is changed according to an image signal in order to adjust an input light amount to the liquid crystal light valve (for example, refer to Japanese Patent Application No. JP-A-5-66501). Further, a projector has also been developed in which a mechanical dimming unit is provided on an optical path from the light source to the liquid light valve (for example, refer to Japanese Patent No. 4158618). The mechanical dimming unit is a unit which opens and shuts a douser, and functions as a diaphragm.
Meanwhile, there is a configuration where a high pressure mercury lamp is used as the light source. When a state where a dimming rate is high is maintained for a long time in the high pressure mercury lamp, a function of a halogen cycle in a lamp declines, and a blackening phenomenon occurs in which evaporated electrode components are precipitated in an inner wall of the lamp. For this reason, there is a problem in that the dimming rate has a certain limit when performing the dimming of the lamp, and it is difficult to sufficiently raise the contrast. Further, there is a problem in that, if the light amount is decreased, an emission spectrum changes, and a color shift occurs, when performing dimming of the lamp.
On the other hand, there is a problem in that an employed material, or a structure of the douser is limited, and it is difficult to reduce the power consumption of the light source, since a load of heat of the douser is large in the mechanical dimming. Further, there is a problem in the mechanical dimming that color unevenness occurs, since a component of oblique light which is input to the liquid crystal light valve changes, when the dimming rate is changed.